4-9-3. Program Message Terminator
A <Program Message Terminator> terminates a se-
quence of one or more definite length <Program
Message Unit> elements. There are three possible
<Program Message Terminator> elements:
1. NL (new line);
2. NL END (EOI); and
3. END (EOI)
NL is defined as a single ASCII-encoded byte
0A (10 decimal). Leading <White Space> elements
are permitted. The instrument interprets any and all
of the three terminators as semantically equivalent.
No alternative encoding are allowed. Note that IEEE-
P981 amendment forbids the use of CR as a <Pro-
gram Message Terminator> element. This is because
some controller treat CR as the end of transmission
and leave the LF character in the unit, thereby
creating an error in the controller.
4-9-4. Command Program Header
The <Command Program Header> represents the
operation to be performed in a device. The header
may be optionally followed by associated parameters
encoded as <Program Data> elements. There are
three defined <Command Program Header> elements:
<Simple Command Program Header>, <Compound
Command Program Header>, and <Common Com-
mand Program Header.
<Simple Command Program Header> is defined
as:
<Program Mnemonic>
For example, FRQ. Leading <White Space> ele-
ments are permitted. Upper/lower case alpha char-
acters are treated with the same semantic equiva-
lence. <Compound Command Program Header> is
not used in model 8020 and will not be discussed
here. A <Common Command Program Header> is
defined as:
*<Program Mnemonic>
For example, *TRG. Leading <White Space> ele-
ments are permitted. Upper/ lower case alpha char-
acters are treated with the same semantic equiva-
lence.
4-9-5. Query Program Header
The <Query Program Header> represents the op-
eration to be performed in a device. A <Query
Program Header> causes the device to generate a
response. This element may be optionally followed
by associated parameters encoded as <Program
Data> elements. There are three defined <Query
Program Header> elements: <Simple Query Program
Header>, <Compound Query Program Header>, and
<Common Query Program Header. A <Simple Query
Program Header> is defined as:
<Program Mnemonic>?
For example, FRQ?. Leading <White Space> ele-
ments are permitted. Upper/lower case alpha char-
acters are treated with the same semantic equiva-
lence. <Compound Query Program Header> is not
used in model 8020 and will not be discussed here.
A <Common Query Program Header> is defined as:
*<Program Mnemonic>?
For example, *CAL?. Leading <White Space> ele-
ments are permitted. Upper/lower case alpha char-
acters are treated with the same semantic equiva-
lence.
4-9-6. Program Data
A <Program Data> functional element is used to
convey a variety of parameter information related to
the <Program Header>.
4-9-6-1. Character Program Data
The <Character Program Data> functional element
is not implemented in Model 8020. Therefore it shall
not be discussed in this manual.
4-9-6-2. Decimal Numeric Program Data
The <Decimal Numeric Program Data> is a flexible
version of the three numeric representations as de-
fined in ANSI X3.42-1975 - NR1, NR2, and NR3.
A <Decimal Numeric Program Data> elements are
defined as:
1. NR1 elements consists of a set of implicit
point representations of numeric values. i.e. (+/-
)12345.
2. NR2 elements are the representations of explicit
point numeric values. i.e. (+/-)12.345.
3. NR3 elements are representations of scaled
explicit radix point numeric values together with an
exponent notation. i.e. (+/-)123.456E(+/-)3.
Model 8020 IEEE-488.2 Operation
Page 4-11
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